1889.] 5d9 [Ryder. 



3. In the birds, or Aves, with the exception of the oil ghind on the tail, 

 there are no integumentary glands which can be compared with those of 

 IheBatrachia. 



4. In the Mammalia the case is very different, for in this group we 

 again for the first time encounter epidermal glandular structures which 

 may be legitimately compared with those in the Batnichia. Aside from 

 the modifications which have resulted from the specialization of the differ- 

 ent layers of the mammalian integument, the only diflerence which the 

 SAveat glands of the latter present in comparison with the epidermal glands 

 of Batrachia are such as may be ascribed to the farther development or 

 progressive evolution of a type of integumentary gland in all structural 

 respects essentially similar to the skin glands of the last-mentioned group. 

 In the next place, the majority of the Mammalia possess integumentary 

 glands which are scattered over the whole of the body. In this respect 

 the Batrachia and mammals are the only forms which essentially agree in 

 the distribution of their integumentary glandular organs other than the 

 mammary, and a few others found in the latter group. The absolute 

 want of a generally distributed integumentary glandular system in the two 

 great groups of Replilia and Aves proves that the phyletic history of 

 these two series is very old, and perhaps almost or quite coeval with that 

 of the Mammalia. It is almost equally certain that the three series. Rep- 

 tilia, Aves and Mammalia, have had a common remote aquatic ancestry, 

 and that the oldest members of that ancestral series had the integuments 

 defended by goblet .cells, followed by a succession of forms in which flask- 

 shaped integumentary glandular organs were developed. Are the exist- 

 ing Batrachia representatives of that series which possessed the simple 

 flask-shaped integumentary glands? Were the Theromora provided with 

 simple saccular integumentary glands ? These are questions still to be an- 

 swered. From all that we know of the integuments of the primitive 

 types of vertebrates, we may assume, Avith every assurance of the legiti- 

 macy of the deduction, that both Reptilia and Aves have probably lost 

 the integumentary glands corresponding to the sweat glands of Mammalia. 



In the Mammalia the sweat glands are characterized by the differentia- 

 tion of a long tubular efferent duct, which has a slightly spiral direction, 

 which becomes more marked where the outer portion of the duct passes 

 through the stratum corneum of the epidermis. At the other end, the 

 simple tubular and properly glandular portion of the gland usually lies 

 in a close coil invested by a plexus of capillary vessels. Or this deep- 

 lying glandular portion may not be so closely coiled, but extend as open 

 loops or irregular bends amongst masses of areolar and connective tissue, 

 as may be well seen in the sweat glands of the ball of the foot of the do- 

 mestic cat, though here, as in other forms, the relation to the blood ves- 

 sels is the same. In all these cases, however, there is essentially the same 

 structure, namely, a lining secretory epithelium and an investment of lon- 

 gitudinally disposed unstriped muscular fibres, an arrangement which can 

 be compared only with the arrangement of the tissues making up the far 

 simpler integumentary glands of the Batrachia. 



